Glow discharge switch



J y 1,952 P. LEMAlGRE-VOREAUX GLOW DISCHARGE SWITCH Filed July 18, 1950lnv'entor Pierre Lemoigre- Voreuux,

y 47 m, hm

Patented July l, 1952 UNITEDLSTATES "Arsinr OFFICE ill 4' 2 3013131 I Iv cr S HAB EI W F- bfi I Pierre Lemaigre-Vo're'aux, Paris,France-,assignorto Societe Ano'n'yme Pour les ApplicationsdelElectricite et des .Gaz Rare's-Etablissement's' Claude-Paz & Silva,Paris, France, a company of France Application July18; 1950, scream-114,500 I In France August '1, 1 949 This invention relates to a glow Idischarge switch for starting and operating gaseous elec tricdischargedevices, said switch being of the type comprising twoelectrodes, a partof one of said electrodes being a bimetallic member which controls aconnection between said two electrodes and which is coated withthermionic emissive materials.

An object of my invention is to provide a new and improved glow switchwhich will close when a'rela'tivel'y low voltage is impressed betweenits terminals and which is easy to manufacture.

Another objectof my invention is to provide a new and improved glowswitch, the closing voltage of which varies little in the course oftime. 1

A further object of my invention is toprovide a new and improved glowswitch of simple design.

A feature of my invention is to connect to the bimetallic member whichcarries the movable contact of the switch a conductor coated with asubstance which, under the effect of a discharge issuing from saidconductor, emits thermionic emissive materials; part, at least, of thesematerials forms a deposit on the bimetallic member and lower the cathodevoltage drop of said member.

Further objects and features of my invention will appear from thefollowing detailed description of species thereof.

The accompanying drawing shows an embodiment of the invention designedfor controlling, according to the well known method of pre-heating theelectrodes, the starting of a gaseous discharge apparatus. The lattermay be, for instance, a fluorescent lamp supplied directly from a 110volt A. C. line, the term directly meaning that the line voltage is notraised or boosted by a transformer or any other device.

The operation of this switch, i. e. its closure under the action on thebimetallic element, of a discharge taking place between the latter orsaid conductor and the fixed contact, should occur under the lowestvalue which the line voltage can assume; on the other hand, it shouldnot occur under the voltage existing between the electrodes of thefluorescent lamp during the normal operation of the latter; in theswitch described hereinafter, the minimum closing voltage is about 80'volts A. C.

This switch comprises, inside an envelope 3 containing a neon atmospherewith 1% argon, under a pressure of about 25 millimeters of mercury, afixed contact 5 and a bimetal element 4 acting as a moving contact;when'cold, the minimum distance between the fixed contact 3 Claims. Q(01. 200%1135) denses on the bimetal element.

and the bimetal element is about 0.5 millimeter. The fixed contact 5 isconnected directly with the outside circuit by its current supply leadincl. 'JI'he bimetal'element 4 is connected with the same circuit throughthe conductor 1 and the current supply lead-in H mounted in series;element is" carried by the support 8 an end of which is inserted in thestem 9 of the envelope, said ste m 'comprisingtan exhaust tube 10 andthe currlent leads 1. and II .passing air-"tight through said stem.

.This arrangement makes it possible to use :a stem 9 comprisingonly :twoilead-in passages. Further, the current which, when the bimetaleleme'n'td. touches. the Jflxed contact 5, .passes thr'ough'stheconductor lfheats up the latter,

I which heats upth'e bimetal'element 4, which delays the moment when thelatter moves away from the contact 5. The period of uninterruptedpre-heating of the fluorescent lamp started by means of the switch, isthus lengthened, which decreases the fatigue of the lamp electrodes.

The conductor 1 is a filament of refractory 'metal, in the shape of adouble-coiled spiral, coated with alkaline earth oxides and alkalineearth metals, like a so-called hot cathode in a fluorescent lamp. It is,in fact, practically, a hot cathode of a normal design which is used asa conductor 1. The formation of this con- 'ductor, i. e. thetransformation of the alkaline earth compounds deposited thereon into amixture of oxides and metals is effected like that of a usual hotcathode; the current leads for this operation are then, one the normallead I l, the other one I, that of the fixed contact.

The connection between the latter and the upper end of the electrode 1is ensured by a heating to about 400 C. of the switch assembly in anoven, a heating which causes a change in shape of the bimetal element 4which then touches the contact 5. The formation of the conductor 1consists in heating it by means of the Joule effect, which causes thedecomposition of the alkaline earth substances; it is accompanied,towards its end, by a production of alkaline earth metals whichevaporate and part of which cong The alkaline earth metals thusdeposited on the bimetalelement in a very thin layer 6 have the effectof lowering the starting voltage for the discharge between the bimetalelement and the fixed contact. When the cold switch, placed in thepreheating circuit of the fluorescent lamp which it should cause tostart, is subjected to a voltage higher than volts, a glow dischargeoccurs between the bimetal element 4 and contact 5 as in usual glowinterruptors with bimetallic electrodes, used for the starting offluorescent lamps by a temporary short-circuiting of the electrodes ofthe latter.

Normally, the glow does not occur on conductor I, probably because ofthe high value of the cold resistance of the oxides coating it. When,after a number of operations, the metal deposit 6 activating the bimetalelement 4 has disappeared or become insufiicient, the glow dischargeoccurs on conductor 7 and partly reduces the alkaline earth oxidescoating it into alkaline earth metals, a part of which is projected bycathodic atmoization on the bimetal element 4 and re-activates it.

Such a switch can operate tens of thousands times Without anyappreciable change in its closing voltage or operating delay. Itsmanufacture on a production scale is easy since the activation processused involves a technique commonly utilized in the industry offluorescent lamps.

I claim:

l. A glow discharge switch of the type comprising in an envelopecontaining a gaseous ionisable medium, a first and a second electrode,at least a part of said first electrode being a bimetallic member forcontrolling a connection between said electrodes and being coated, atleast partly, with thermionic emissive material, said switch comprisingin the envelope a conductor, connected with said first electrode andcomprising a refractory metal wire winding coated with materialscontaining at least one alkaline earth metal and the vapor tension ofwhich is negligible at the maximum electrodetempcrature, said conductoremitting emissive material when a discharge starts from it, at leastpart of the material so emitted depositing on the bimetallic member.

2. A glow discharge switch of the type comprising, in an envelopecontaining a gaseous ionisable medium, a first and a second electrode,at least a part of said first electrode being a bimetallic member forcontrolling a connection between said electrodes and being coated, atleast partly, with thermionic emissive material, a first and a secondlead-in wire, respectively for the first and the second electrode, saidswitch comprising in the envelope a conductor, connected in seriesbetween said first lead-in wire and said first electrode and coated withat least one substance, the vapor tension of which is negligible at themaximum electrode and conductor temperature and which, when a dischargestarts from said conductor, emits said emissive material, at least partof the material so emitted depositing on the bimetallic member.

3. A glow discharge switch according to claim 2, the winding being inthe form of a helical coil at least singly coiled and being made up ofat least one wire, and the materials coating said winding comprising atleast one alkaline-earth oxide.

PIERRE LEMAIGRE-VOREAUX.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,251,278 Hays, Jr., et al Aug.5, 1941 2,280,550 Smitley Apr. 21, 1942

